1. Field of the Invention
This invention relates to the design of a suspension loadbeam to support slider mounted read/write transducers in disk drives. More particularly, it relates to a loadbeam design that provides superior dynamic performance during drive operation.
2. Description of the Related Art
A hard disk drive (HDD) uses an encapsulated thin film magnetic read/write head (transducer), called a slider, to read and write data on a magnetic medium or storage disk. The slider has a pre-patterned air-bearing surface (ABS) and is mounted on a flexible head gimbal assembly (HGA) that is itself mounted on a loadbeam. The combination of the loadbeam, the gimbal assembly (also referred to as a flexure), the electrically conducting leads (or traces), a hinge mechanism and a baseplate, is collectively termed the suspension. The suspension is activated by a servo actuator and associated electronic control circuitry to position the slider at various target locations along the magnetically encoded tracks on the disk. As the disk is rapidly rotated by a spindle motor, hydrodynamic pressure causes an air flow between the ABS of the slider and the surface of the disk. This flow, called the air-bearing layer, lifts and suspends the slider so that it literally flies above the surface of the disk (at a “fly height” of approximately 10 nm) on a layer of air called, appropriately, the air-bearing layer. The edge of the slider into which the disk rotates is called its “leading edge,” the opposite edge, which contains the read/write head is called the “trailing edge.” The loadbeam, as is known in the art, has a small protrusion or “dimple” formed on its disk-facing side that presses against the backside of the slider, providing a downward force and a pivot point for the slider to rotate about. This suspension system of loadbeam and flexure provides mechanical support for the slider while also allowing the slider pitch and roll capability when fly height is achieved. In addition, the system provides an electrical connection (i.e., a placement for the routing of conducting traces) between the read/write head and the pre-amplifier.
Enabling the slider to fly in a stable manner above the disk places stringent requirements on the suspension design, such as providing a proper range of its vertical stiffness (Kz), gimbal pitch and roll stiffness (Kp, Kr), gimbal pitch/roll static attitude (PSA/RSA), operational shock performance (G/gram) and the like. These requirements are mainly static and based on system geometry. A further requirement is that the suspension have little or no dynamic effect on the air bearing performance of the slider when the drive is operational. This requirement is related to the dynamic performance of the suspension. In general, dynamic performance requirements are not always enforced, so the dynamic performance of many existing suspensions is not good.
FIG. 1 shows the response of a slider striking a bump on a spinning disk under conditions that do not include dynamic effects of the suspension (i.e., the slider is not dynamically coupled to the suspension). The graph plots the vibrational response (air bearing modes) of the slider in a wide frequency range and shows that there are only two peaks in this response. The modes are strongly damped, producing a small vibrational amplitude and the slider settles down quickly.
FIG. 2 shows a suspension mounted slider also striking a bump on a disk, but in a situation where the dynamic effects of the suspension now have a strong influence on the subsequent slider response because the slider and loadbeam suspension are dynamically coupled by the air-bearing layer. As can be seen, the response curve now displays many sharp peaks, which are the result of loadbeam/slider air bearing coupling modes. Those modes at low frequencies that are not well damped (the sharp peaks) make it difficult for the slider to relax to an equilibrium condition. They can even cause the air bearing condition to become unstable and generate a sustained vibration. Under such circumstances the disk drive will fail or, at the least, its performance will be seriously degraded.
Recent studies have shown that the design of the loadbeam can play an important role in slider dynamic response. This is especially true if a thin and mass-reduced loadbeam is used to achieve a high operational shock performance. FIG. 3b shows a slider response curve for a slider that is part of a suspension system that includes an existing loadbeam design (shown in FIG. 3a) that is thin (25 microns in thickness) and mass reduced through the use of strategically placed cut-outs. Except for the gimbal related peak at 57 kHz, the remaining three peaks are loadbeam related.
The prior art discloses several approaches to improving the performance of a suspension. Schulz et al. (U.S. Pat. No. 6,977,798) teaches the lamination of a specific composite material to the steel structure of load beam as a way of stiffening the load beam. The composite stiffeners are bonded to steel layers by an adhesive and cover most of the area of the loadbeam including the baseplate area. The loadbeam is then shaped after its composite layer and steel layer lamination has been formed. The purpose of the composite stiffeners is not to eliminate specific vibrational modes and resonances induced by HDI interactions, but rather to stiffen the entire suspension in response to aerodynamic forces.
Albrecht et al. (U.S. Pat. No. 6,914,752) teaches the use of a continuous contact slider, wherein the flexure must provide a moment to counteract the moment generated by the adhesive force between the disk and the slider's contact pad.
Xu (U.S. Pat. No. 6,900,966) teaches the stiffening of a load beam by means of welding together pieces of the load beam at weld pockets, rather than using spot welds.
Karam II (U.S. Pat. No. 5,408,372) teaches the stiffening of a load beam by the addition of material or by crimping the beam at locations on the beam near its flexible end. Karam is basically interested in eliminating very low frequency vibrations, between 1-10 kHz and does so by stiffening between the dimple and hinge of the suspension.
Zhou et al. (U.S. Patent Application 2006/0028767) teaches the formation of a stiffening rail by bending the load beam. The loadbeam of the invention uses no flexure, so all of the shocks to the suspension must be absorbed by the beam itself.
It is clear from a reading of the prior art cited above that there is a need to improve slider response to vibrational motion produced by head-disk interface (HDI) interaction of a loadbeam mounted slider with disk asperities (i.e., bumps and other deviations from disk planarity) while the disk is in rotational motion.